Like Alzheimer's disease (AD), the prion diseases are age-dependent degenerative disorders of the central nervous system (CNS). These dementing diseases are among the most dreaded afflictions from which older people frequently suffer. Studies on both the familial and sporadic forms of AD have been slow, in part, due to our lack of suitable animal models. In contrast, the availability of animal models for neurodegenerative diseases caused by prions has led to relatively rapid advances. Indeed, prion diseases have become the most well understood CNS degenerative disorders of delayed onset and they are the focus of this proposal. In humans, prion diseases generally occur in order adults but the mechanism governing their time of onset is unknown. An enlarging body of evidence argues that prion diseases are disorders of protein conformation. Investigations directed toward elucidating the role of molecular chaperones in the conversion of the cellular prion protein (PrPC) into the scrapie isoform (PrPSc) are proposed (Project 1). These studies extend recent findings showing that scrapie infection of cultured cells is accompanied by a profound change in the stress response; many stress proteins appear to function as chaperones. Studies of prion infected cultured cells also suggest that alterations in membranes, as manifest by changes in Ca2+ transport and lipid flux, may underlie the neuropathology of these disorders (Project 2). The neuropathology of experimental prion diseases in mice has been known for many years to be controlled, at least in part, by "strains" or different isolates of prions. Investigations of prion strains focus on one of the most challenging and enigmatic aspects of these disorders. Whether individual strains of prions represent different conformers of PrPSc remains to be established. To test this hypothesis, several new approaches to studies of the molecular basis of prion strains are proposed including the use of transgenic (Tg) mice expressing chimeric Syrian hamster (SHa)/mouse (Mo) PrP genes as well as Tg and PrP gene targeted hamsters (Project 3). The higher concentrations of PrPSc in SHa brains offer an important advantage in protein structure studies while the mice expressing chimeric SHa/Mo PrP transgenes allow the transfer of Mo prion strains into hamsters. These investigations are closely tied to investigations of PrP structure which utilize recombinant and solid phase synthesis of large peptides as well as full length proteins for analysis by spectroscopy, bioassays of scrapie infectivity (Project 4) and NMR (Project 5). Determining the structures of PrPC and PrPSc by solution and solid state NMR are important goals of this application. The diverse skills, talents and backgrounds of the investigators in the proposed program offer an unusual opportunity to define the molecular mechanisms responsible for neurodegeneration in prion diseases. Elucidation of the mechanisms by which brain cells cease to function and die in prion diseases after a long delay may offer new approaches to elucidating the etiologies of more prevalent neurodegenerative disorders afflicting older people, including AD.